My doctor told me that magnesium is a relaxant for the muscles...hence sleeping well and possibly relief from uterine (a muscle) cramps. How much do you take? I can take over 1000 mgs without diarhhea. You might want to think of it as, if you DON'T have diarhhea, you might not be getting enough. I was told to take more and more until my body is saturated to be sure. (Same philosophy about taking Vitamin c; diarhea is the signal your body has had enough...up to that point your body is using it).
Hyaluronic acid is not cheap, so I'd experiment with mag to see if it works. However, I'm so pleased with the HA for other reasons, so I don't want to talk you out of that. Let me know if it works for you.